This is a revised Phase II application based on 2006 application and reviewers' comments. In this version, we made significant modifications, including: change the two rings cathode design to three rings structure, adding the synchronization gating control effort, and details of the processing and manufacturing of the carbon nanotube (CNT) cathodes and x-ray tubes. During this period, we achieved dramatic progress on the CNT x-ray technique, which makes us confident the success of this development. [unreadable] Substantial technological growth has spurred a new interest in imaging techniques, and their usage has grown considerably. High-resolution small animal imaging systems have emerged as important new tools for laboratory animal research. X-ray imaging is widely used in diagnostic radiology, biomedical research and a wide variety of industrial applications. We propose to design and construct a portable, low cost micro-focus x-ray tube using the carbon nanotube (CNT) field emission source as the cathode to overcome disadvantages of the hot electron sources in the present x-ray tubes. After Phase II, we expect to be able to develop the CNT field emision micro-focus x-ray tube with the following features: spatial resolution (effective focal spot size): adjustable with 10 5m, 30 5m, and 100 5m three levels; temporal resolution: adjustable, from 0.1 to 100 ms; X-ray tube current: adjustable, up to 2 mA peak current at 100 5m resolution; anode voltage: 40-60 KVp; synchronization gating control; and lifetime: up to 3000 hours. The primary application of the proposed x-ray source is for small animal imaging related medical research and diagonosis. [unreadable] The major research design and methods to achieve the proposed development goals include: 1) Construction of the micro-focus x-ray tube with resolution of 30 5m based on Phase I study; 2) Development of the compact CNT field emission 10 5m micro-focus x-ray source meeting key Phase II targets; 3) Design and assembly of the compact electronic control system for the x-ray source of Aim 2; 4) Construction of a sealed and portable micro-focus x-ray tube with the specifications of Aim 2; and 5) Demonstration of the high resolution dynamic micro-CT imaging. [unreadable] [unreadable] [unreadable]